A great number of civil engineering structures are supported by cables, in particular, but not exclusively, cable-stayed bridges and suspension bridges.
These cables are generally anchored to the civil engineering structure by anchor means that are similar to an end-fitting, possibly imperfect. Consequently, the cables, in addition to being subject to longitudinal tensile forces, are subject to parasitic bending forces, which create local bending stresses.
The cables are subject to various types of loads, in particular, what are known as static and dynamic loads.
Static loads are generally due to slow changes, for example, changes in temperature or overall changes of the load on the civil engineering structure.
Dynamic loads correspond to more rapid changes, for example, wind gusts or the passage of a truck over the civil engineering structure.
The stresses that result from these loads, even if they are below the resistance of the cable, can lead to rupture of said cable if they are repeated too many times. In this case we speak of fatigue failure of the material constituting the cable.
There are calculation guidelines that can be used to verify that cable dimensions are compatible with the loads to which the structure is liable to be subjected during its lifetime.
Generally, these calculation guidelines consist, initially, in determining the fatigue capital, or the initial capital of the cable. Subsequently, we evaluate the loads the structure will be subjected to during its lifetime as well as the frequency of those loads. Finally, we make sure that those evaluated loads only partially consume the initial capital of the cable.
The cables are subject to fatigue, primarily in their anchorage zone, where fluctuations in tensile loads or axial stress are added to bending stress. Bending stress can be significant, for the cable experiences angular variations, as a result of which said cable is not perfectly aligned with its anchorage. The fluctuation of this anchorage angle due to movement of the structure, to cable vibration, or to the alteration of its catenary arc associated with variations in tensile load, result in bending stresses that are variable and significant.
While calculations can be used to evaluate the fatigue damage to cables and, thus, their lifespan during the design stage, these calculations are limited by the initial assumptions.
For example, in the case of a bridge, cable fatigue associated with automobile traffic on a bridge is based on estimates that can be exceeded over time.
Moreover, dynamic effects associated with the passage of convoys, especially truck convoys, are currently not fully taken into account during calculations. Finally, some dynamic effects, associated with the condition of the roadway, are simply not predictable.
Moreover, the dynamic effects of wind are hard to quantify. Vibrations, their amplitude and frequency of occurrence are largely unknown during the design of the system.
Therefore, it is useful to be able to follow the evolution of the initial fatigue capital of the cable supporting a structure during the life of said structure.
In this way, maintenance or upgrading activities can be planned in the event of the abnormally rapid consumption of fatigue capital or whenever it is nearly exhausted.
An object of the present invention is to provide a method for determining the fatigue capital of a cable supporting a civil engineering structure.